The present invention relates to fittings and, in particular, to fittings for mobile air conditioning systems.
Mobile air conditioning systems provide summertime comfort to millions of automobile drivers and passengers on the road. The air conditioning system typically circulates a refrigerant, applying work in a well-known thermodynamic cycle to remove heat from the refrigerant prior to circulating it into the passenger compartment of the vehicle. Circulating the refrigerant in and out of the vehicle and through the refrigeration system components requires many fittings that interconnect the components, typically through hoses and tubes. In a mobile air conditioning system, the fittings must be sufficiently robust to withstand the rigors present in the engine compartment of a moving vehicle, without loosening or otherwise enabling the refrigerant to leak from the system. The fittings must also be removable to permit the system to be appropriately maintained. Due to the dynamic, thermal, and chemical environment within the engine compartment, regular maintenance of the mobile air conditioning system is essential.
Many of the fittings used in mobile air conditioning systems, particularly those used in Class 8 trucks, comply with a standard published by the Standards Committee of the International Mobile Air Conditioning Association, Inc., the standard known in the industry as the IMACA 305 Standard. For purposes of the present disclosure, the term xe2x80x9cIMACA 305 Standardxe2x80x9d means the standard described in xe2x80x9cIMACA Component Standard 305 Fittings and Tubing Details for Mobile Air Conditioning Systems,xe2x80x9d copyrighted 1997 by International Mobile Air Conditioning Association, Inc. The MACA 305 Standard defines a physical standard covering details for threaded connections and tube end forms for flare and O-ring type connections, as well as hose insert details for barb style fittings for mobile air conditioning systems.
FIG. 1 illustrates an exploded view of a typical fitting assembly 50 complying with the IMACA 305 Standard. The fitting assembly 50 includes a tubular male fitting member 52 that sealingly engages a female fitting member 72. The male fitting member 52 (see IMACA 305, FIG. 7A, Option 1) includes a tubular proximal portion 54, a tubular distal or pilot portion 56, and a circumferential bead 58 disposed between the proximal portion 54 and the pilot portion 56. A swivel nut 60 slidably engages the proximal portion 54 and is restrained from sliding off the distal end of the pilot portion 56 by the circumferential bead 58. The swivel nut 60 comprises a conventional hexagonal portion 62 with a threaded orifice having an inside diameter greater than the diameter of the circumferential bead 58, so that the threaded portion can slide over the circumferential bead 58 and a smaller diameter neck portion 64 that engages the circumferential bead 58 when the fitting assembly 50 is properly assembled.
The female fitting 72 shown in FIG. 1 (two-piece construction shown; a rigid, one-piece construction is also acceptable per IMACA 305 Section 5) includes a tubular proximal portion 74, a tubular intermediate portion 75 having an inside diameter selected to slidably receive the male fitting pilot portion 56, and a tubular distal portion 76 having an inside diameter that is larger than the intermediate portion 75 to accommodate an O-ring 51 between the pilot portion 56 and the distal portion 76. A swivel nut 80 having outer threads 83 adapted to engage the male fitting swivel nut 60, is slidably disposed on the proximal portion 74 and retained from sliding over the distal end of the female fitting 72 by the intermediate portion 75 and/or the distal portion 76. The swivel nut 80 includes a conventional hexagonal portion 82 to facilitate installation and disengagement of the fitting assembly 50. The O-ring 51 is provided between-the male fitting 52 and the female fitting 72 to substantially seal the connection when the fitting assembly 50 is properly assembled.
FIG. 2 presents a partially cut-away view of the assembled fitting assembly 50. It will now be appreciated that fitting assembly 50 is releasably engaged by inserting the pilot portion 56 of the male fitting 52 into the distal portion 76 of the female fitting 72 and into the intermediate portion 75. The IMACA 305 Standard defines the pilot portion""s 56 outside diameter as nominally 0.001 inch smaller than the nominal inside diameter of the intermediate portion 75. The male fitting 52 is inserted into the female fitting 72 until the circumferential bead 58 abuts against the distal portion 76 of the female fitting 72. The O-ring 51 in the assembled fitting 50 is compressed between the pilot portion 56 and the female fitting 72 distal portion 76. The swivel nuts 60, 80 are engaged to bring and hold the male and female fittings 52, 72 tightly together.
The O-ring 51 provides a seal between the female fitting 72 and the male fitting 52 to prevent the leakage of refrigerant from the connection. The region between the male fitting 52 and female fitting 72 that receives the O-ring 51, is frequently referred to as the O-ring xe2x80x9cglandxe2x80x9d and is detailed in isolation in FIG. 3. The gland 65 is shown with the O-ring 51 in phantom. It is now clear that the distal portion 76 of the female fitting 72 is larger in diameter than the intermediate portion 75 in order to accommodate the O-ring 51. To achieve an optimal and reliable sealed connection, the O-ring 51 must be compressed in the gland 65 a suitable amount such that a seal is produced against both the inner surface of the distal portion 76 and the outer surface of the pilot portion 56.
It is also noted that the fitting depicted in FIGS. 1xe2x80x943 is defined in various sizes in the IMACA 305 Standard and with various pilot portion 56 lengths, the two-dimensional size of the gland region shown in FIG. 3 is generally the same for all of the defined connection sizes. In particular, the width of the O-ring aperture between the female fitting distal portion 76 and the male fitting pilot portion 56, denoted as W in FIG. 3, is nominally 0.135 inch (per IMACA 305, FIG. 5B, Table 5B), and the corresponding depth, denoted as D in FIG. 3, is nominally 0.0445 inch (derived from dimension in IMACA 305, FIG. 5B, Table 5B) (the distal portion 76 is nominally flared 5xc2x0, denoted as angle A in FIG. 3, so the depth varies slightly across the width).
Although the illustrated fitting assembly 50 utilizes a two-piece female fitting 72 (including the swivel nut 80), many straightforward alternative configurations;are utilized in the industryxe2x80x94including, for example, an alternative assembly described in the IMACA 305 Standard wherein a one-piece rigid female fitting is utilized with the interior of the nut portion of the female fitting having substantially the same geometry as the interior of the tubular portion of the female fitting 72 shown in FIG. 1., Similarly, although FIGS. 1 and 2 show an embodiment wherein the pilot portion 56 is smaller in diameter than the proximal portion 54, other configurations are possible, including, for example, configurations described in the IMACA 305 Standard wherein the pilot portion is larger in diameter than the proximal portion.
Although FIGS. 1 and 2 show the fitting assembly 50 in a horizontal orientation, in many applications the female fitting 72 is oriented vertically or at an angle of inclination, with the distal portion 76 facing upwardly. The vertically oriented fitting assembly 50 is assembled by bringing the male fitting 52 downwardly to engage the female fitting 72. In connecting the fitting assembly, the O-ring 51 is typically first lubricated with an appropriate lubricant and then slid over the pilot portion 56 of the male fitting 52 until it is adjacent the circumferential bead 58. The male fitting 52 is then inverted and inserted into the female fitting 72. In actual practice, it has been found that during such assemblies, the O-ring 51 frequently slides downwardly during the assembly process, which can result in loss or damage to the O-ring 51 during assembly. Moreover, damage or loss of the O-ring 51 may not be apparent during the installation, particularly in the common situation wherein the fitting assembly is in a location having relatively limited access. Damage or loss of the O-ring 51 is very undesirable because, if the joint is not properly sealed, then the refrigerant can escape from the air conditioning system, preventing the air conditioner from operating properly and releasing refrigerant into the environment. It will also be readily apparent that even in horizontally-oriented connections, the male fitting 52 may be inverted temporarily during assembly, permitting the O-ring 51 to slide toward the distal end of the pilot portion 56 and resulting in similar loss or damage to the O-ring 51.
Other fitting assemblies have been designed for mobile air conditioning systems that are intended to avoid or overcome the risks associated with loss or damage to the O-ringxe2x80x94including, for example, fittings utilizing flanged joints, grooved pilot tubes, and/or bonded washer joints. These alternative fittings, however, are not compatible with the many existing IMACA 305 Standard compliant fittings in service on existing automobiles, and therefore may require expensive retrofitting of existing equipment in order to implement. Additionally, such alternative designs are typically more difficult to assemble, and may require special tooling to assemble.
There remains a need, therefore, for an improved mobile air conditioning fitting that reduces the risk of damage or loss of the O-ring and that is compatible with the fittings on existing equipment.
An improved fitting for mobile air conditioning systems is disclosed that reduces the risk of loss or damage to the O-ring while maintaining compatibility with the large number of existing equipment currently in service. The improved fitting also connects in the same way as existing prior art connections so no new training or tools are required. Fittings for mobile air conditioning systems typically comprise a male member and a female member, the male and female members defining a gland therebetween for accommodating an O-ring, in order to provide a sealed connection. The O-ring is placed around the fitting male member prior to assembly and the male member is inserted into the female member and tightened using mating-threaded members to form a tight connection. In prior art fittings, the O-ring can slide along the male member, which can lead to loss or damage to the O-ring and subsequent leakage of refrigerant. In the present invention, a retainer bead is formed on the male member to retain the O-ring in the proper position. The retainer bead is sized and positioned to retain the O-ring without interfering with proper compression of the O-ring, and without interfering with the full assembly of the male and female members.
In an embodiment of the present invention, the retainer bead has a height between about 0.013 inches and 0.017 inch, a width between about 0.0471 inch and 0.0477 inch, and spaced axially from the circumferential bead between about 0.102 inch and 0.106 inch.
In another embodiment of the present invention, the retainer bead has a height of about 0.015 inch, a width of about 0.0474 inch, and is spaced axially from the circumferential bead by about 0.104 inch.